Generally, chip elements such as chip resistors, chip inductors, and chip capacitors each formed as a chip are widely used as components to be mounted on printed wiring boards. Such chip elements can improve a mounting density per unit area.
Those components are each completed by forming a wiring structure, adapted to realize its function, on a ceramic substrate of alumina, ferrite, or the like, covering the wiring structure with a glass, a resin, or the like, and forming electrodes at end portions of the wiring structure.
The reason for using the ceramic as a packaging material covering the wiring structure is to provide heat resistance against a high temperature process at 200° C. to 300° C., such as a solder reflow process, performed at the time of mounting on a printed wiring board of glass epoxy, or the like.
Further, such a chip element is mounted on a printed wiring board and used, for example, as a terminal resistor of a microstrip line widely used as a signal transmission line, or the like, or as a matching element for high-frequency signals of a portable telephone or the like. In this case, 50Ω is generally used as a characteristic impedance of the foregoing signal transmission line.
On the other hand, in order to supply a sufficient signal to wiring of such a 50Ω system from an active element such as an LSI, for example, buffer circuits are formed at input/output portions of the LSI and a large current is generated by the buffer circuits, thereby driving the wiring of the 50Ω system.
In any event, it is expected that chip elements of this type will be used in a higher frequency region, i.e. even in a frequency band of 1 GHz or more.
On the other hand, as chip elements of this type, there are those described in Japanese Unexamined Patent Application Publication (JP-A) No. H11-162719 (Patent Document 1), Japanese Unexamined Patent Application Publication (JP-A) No. H10-233302 (Patent Document 2), and Japanese Patent (JP-B) No. 2739334 (Patent Document 3). Among them, Patent Document 1 discloses a chip resistor in which a resistor and two electrode terminals connected to the resistor are insert-molded with a thermosetting unsaturated polyester resin. On the other hand, Patent Document 2 discloses a chip resistor in which a base electrode and a film resistor made of ruthenium oxide are formed on an insulating chip substrate made of a liquid crystal polymer. Further, Patent Document 3 discloses an impedance element that uses a magnetic material extrusion-molded from a magnetic paste obtained by mixing and kneading a ferromagnetic powder, a binding resin, and a solvent, and a manufacturing method thereof.
However, it has been found that there arises a problem that the impedance changes from a design value in a high frequency region of 1 GHz to 10 GHz in the case of a conventionally used chip element, particularly a chip resistance element or a chip inductance element.
This problem is remarkable particularly in a high resistance region exceeding 100Ω in the case of the chip resistance element and is remarkable particularly in a high inductance region exceeding 1 nH in the case of the chip inductor element.
Patent Document 1 discloses the chip resistor excellent in heat resistance and molding efficiency and its manufacturing method, wherein the resistor is insert-molded in the thermosetting unsaturated polyester resin. Therefore, Patent Document 1 suggests nothing about using the chip resistor in a GHz band and thus does not indicate a measure therefor.
Further, Patent Document 2 proposes to use the liquid crystal polymer chip substrate for suppressing an increase in cost when a ceramic substrate is used, but this Patent Document 2 also suggests nothing about using the chip resistor at high frequencies of a GHz band and a problem in that event.
Patent Document 3 has no description about a particle size of the magnetic powder and a permittivity of the resin that are necessary for making high frequency characteristics excellent, suggests nothing about an impedance element for use at high frequencies and thus does not indicate a measure therefor. Further, since a conductor layer is extrusion-molded, there arises a problem that a complicated circuit pattern such as a coil cannot be formed.